The lighting arrangement should be such as to provide sufficient illumination, uniform distribution of light, and avoid glare and shadow for designing the lighting scheme, the following factors should be taken into consideration.
1. ILLUMINATION LEVEL:-
This is the most vital factor because, sufficient illumination is the basic means by which we are able to see our surroundings. It is the task of illumination to give objects a distributed brightness with minimum fatigue depends upon.
i) The size of the object to be seen and its distance from the observer, the greater the distance of the object from observer, smaller the size of objects.
ii) Contrast between the object and its background.
Greater the contrast between the colour of the object and its background, greater will be the illumination required to distinguish the object properly. Objects which are seen for longer duration of time require more than those of casual work. Similarly moving objects require more illumination than those of stationary objects.
2. SPACE HEIGHT RATIO:-
It is defined as the ratio of horizontal distance between lamps and the mounting height of lamps
Space height ratio=( Horizontal distance between lamps/ Mounting height of lamps)
In order to have uniform illumination, it is necessary that the value of this should be properly chosen and this may vary between 1 and 2.
3. UTILIZAION FACTOR:-
The total light flux radiated out by the source is not utilized on the working planes and utilization factor is given as,
Utilization factor= ( Illumination under normal working conditions/ Total lumens radiated by lamp)
The value of this coefficient depends upon the following conditions,
a) The area to be illuminated.
b) Height at which lamps are fitted.
c) The colour of surrounding walls, ceiling, fittings etc.
d) The type of lighting i.e, direct or indirect.
The value for direct light varies from 0.25-0.5 while the value for indirect light varies from 0.1-0.3.
Higher the value of utilization factor, more lumens will reach the working plane for given lumens output of the lamps.
4. WASTE LIGHT FACTOR:-
A surface when illuminated by number of lamps, there is vertain amount of wastage due to overlapping of light waves. Its value for rectangular and irregular areas are 1.2 and 1.5 respectively.